Decarbonisation of humidification in commerical buildings

Author: Darren Bryant

Area Sales Manager, UK

Article summary

EPC-B rating needed

Buildings with gas-fired humidifiers will find it difficult to meet the Minimum Energy Efficiency Standards.

Electric humidifiers popular

Using electric steam humidifiers rather than gas-fired reduces a building's reliance on fossil fuels.

Evaporative cooling benefits

Exhaust air evaporative cooling AHU strategy can reduce a building's cooling energy use by over 50%.

Decarbonisation of humidification in commerical buildings

Darren Bryant, Area Sales Manager at Condair, looks at how a commercial building using humidifiers can reduce its carbon footprint for humidity control and cooling.

Many commercial building operators are actively pursuing strategies to reduce carbon emissions to achieve the required Energy Performance Certificate (EPC) in time for the forthcoming regulatory changes. Current government targets are for all leased commercial buildings to have an EPC B-rating by 01/04/2030, although it’s expected this date may be shifted to as late as 2035.

So, what does this mean for humidification systems and what preparations, if any, are required to maintain the optimum indoor humidity whilst meeting the Minimum Energy Efficiency Standards (MEES)?

Any building operating gas-fired systems will find it increasingly difficult to achieve an EPC B-rating, given their reliance on fossil fuels. Gas-fired steam humidifiers have been popular across the UK, particularly in buildings needing high-capacity humidification. They offer big outputs with lower energy costs than electric steam humidifiers, as gas is obviously cheaper per kW than electricity.

We’ve recently seen many clients replacing gas-fired humidifiers with electric steam humidifiers, as they can be operated on renewable energy, thus reducing overall carbon emissions. The retrofit is a relatively simple swap, as the same space is required in the AHU. In fact, it’s likely the legacy steam distribution systems can be left in the AHU, reducing installation costs and complexity.

However, as gas-fired humidifiers offer large outputs from a single unit, it’s likely the overall footprint of an electric system is going to be larger than the gas unit it is replacing. This needs to be considered during project planning. Replacing a 320kg/h gas humidifier may require three or four electric humidifiers to offer the same output. Luckily humidification systems of this size are often on roofs, which may alleviate this concern.

But if plantroom space is limited, or if the amount of available electricity is not sufficient to meet the needs of an electric steam system, adiabatic humidifiers might offer a practical alternative. Cold water humidifiers mounted inside the AHU can offer high outputs but do need pre-heating prior to the humidifier section. The air-on condition needs to be dry enough to absorb moisture from the humidifier. This pre-heating typically comes from a heater coil attached to a gas boiler. Unfortunately, this doesn’t help our carbon reduction goal, as the overall energy and carbon emissions in this circumstance will be identical to the gas-fired humidifier we’re looking to replace.

However, often decarbonisation initiatives involve replacing gas boilers with heat pump chillers, alongside exchanging other gas-fired systems. If this is the case, and the heating prior to the adiabatic humidifier can be achieved with a heat pump, the overall electrical load will be much less than using self-generating electric steam humidifiers due to the heat pump’s COP. As the adiabatic humidifier itself uses a very small amount of energy to simply circulate water, employing it in combination with a heat pump chiller, could result in the energy consumption being three times lower then self-generating electric steam humidifiers for the same humidity output.

Adiabatic humidifiers, such as the Condair ME, also offer excellent opportunities to reduce a building’s cooling energy consumption with associated carbon reductions. An evaporative humidifier will deliver 0.68kW of cooling for every 1kg of water evaporated. As a single unit will operate on less than 1kW of electricity whilst evaporating up to 1,000kg/h of water, the potential for low energy, high-capacity cooling is significant if it can be effectively employed.

Using direct air evaporative cooling (DEC) strategies to cool commercial buildings, rather than mechanical cooling, has a very limited potential. Buildings need to maintain mid-range indoor humidity levels, which a DEC strategy would struggle to do, and it relies on favourable outside air conditions for the water to evaporate. However, modern indirect AHU strategies, such as Exhaust Air Evaporative Cooling (EAEC), avoid both these limitations and offer consistent cooling performance.

Rather than humidify and cool the incoming airstream, an EAEC system cools the extract air from a room with an evaporative humidifier. The return air has a relatively stable condition and can be humidified close to saturation to achieve the highest possible cooling effect. This cool wet return air is then fed through a heat exchanger before being vented externally. The heat exchanger transfers the cool thermal energy to the incoming airstream, cooling it by up to 10K.

As the humidity increase is only on the return air, there is no impact on indoor humidity levels. The efficiency of an EAEC system does rely on the heat exchanger, but even with a modest 70% HX efficiency, a typical building in London could reduce its reliance on mechanical cooling by around 40% with this strategy. Whilst it’s not a universal solution, EAEC offers real and achievable benefits for energy reduction and decarbonisation initiatives.

Decarbonisation is being driven by legal regulation and financial risk. Upgrading heating, cooling and humidification systems will soon not be optional for any landlord, as failing to meet the Minimum Energy Efficiency Standards will mean a building cannot be legally leased. Given the number of properties needing to make improvements, as the deadline approaches it’s likely that competition for labour and building products will increase.

Early planning could avoid regulatory penalties and lost rental revenue. Condair offers free, expert advice for any building operator or facilities manager looking to explore their humidification or evaporative cooling options to help meet or exceed the EPC B-rating prior to the deadline.